Tissue - Epithelial Flashcards
Major differences between Epithelial tissue and connective tissue
- Number of cells in tissue - epithelial has more cells tightly packed in the extracellular matrix
- Epithelial has no blood vessels - exceptions connective tissue having a large network (except cartilage) and epithelial lining
How do epithelial tissue and connective tissue relate to each other?
Epithelial tissue being avascular is often next to connective tissue which has a network of blood vessels. Thus, epithelial tissue and connective tissue can exchange substances when Exhange with blood is necessary = oxygen, nutrients and waste.
Arrangement of epithelial tissue
Single of multiple layers of sheets. Forms covering and lining in body. Not covered by another layer - has a free surface. Apical (free_ surface and basal surface bottom - polar.
Major purpose of epithelial tissue
Protect , absorb, filtrate and secrete. Selective barrier.
How are epithelial tissue classified ?
- Based on arrangement of cells in layer.
- Cell shape
Types of arrangement of cells in + desciption in regards to epithelium cells
- Simple epithelium - single layer, diffusion, filtration, secretion and absorption.
- Pseudostratified epithelium - single layer, nucleus different levels and cells don’t always reach apical surface. Can have cilia or goblet cells that secrete mucous.
- Stratified epithelium - more than two layers, protect underlying tissue in locations where wear and tear.
Types of cell shape + description
- Squamous - flat and thin, allow for rapid passage through them
- Cuboidal - tall as they are wide like cubes or hexagons. Can have microvilli on apical surface which secretes and absorbs.
- Columnar - taller than wide. Protect underlying tissue. Apical surface can have cilia or microvilli, often specialized in secretion and absorption.
- Transitional - change shape
Simple squamous
- Single flat layer
- Centrally located nucleus
- Oval or spherical in shape
- Filtration (blood in kidneys) and diffusion (oxygen into blood vessels) and secretion (at serous membranes)
- Not found at a site that undergoes mechanical stress
- Found in cardiovascular and lymphatic system
Simple cuboidial
- Sinele layer, cube shaped cells
- Nucleus centrally located
- Secretion and absorption
- Some glands such as thyroid and lines capsule of the eye
Simple columnar
- single layer of column
- oval nucleus near base
- can have microvilli (increasing rate of absorption)
- Can have goblet cells, which secrete mucous
- Lines gastrointestinal tract, duct of many glands.
Pseudostratified columnar
- appear several layer because nuclei are various levels
- all cells attached to basal membrane
- some cells do not extend to apical surface
- Can have goblet cells or cilia
- Secrete mucous (if ciliated), and sweep mucous away
- No cilia- absorption and protection
- Line upper respiratory tract, line duct of many glands, part of male urethra.
Stratified squamous
- 2 or more layers
- Cells deeper may be more cuboidal and columnar
- as basal cells divide, cells push up to apical layer
- as they move to the top, blood supply decreases, become more dehydrated and less metabolically active.
- tough proteins start to dominate, cells become tough
- at apical surface, cells are dead
- Keratinized - at apical layer mainly - protects skin and underlying tissue from heat, microbes and chemicals
- Non-keratinized - moistened by mucous from salivary and mucous glands
- Keratinized - superficial layer of skin
- Non keratinized esophagus, and covers tongue
- protects (abrasion, heat, UV ) and defense against microbes
What type of epithelia tissue can could be keratinized or not ?
Stratified squamous
Stratified cuboidal
- two or more layer
- cells in apical layer more cube shape
- protection, limited secretion and absorption
- rare
- ducts of adult sweat gland and esophageal glands
Stratified columnar
- Basal layer usually shorter and irregular shaped cells
- Only apical layer columnar
- rare
- protection and secretion
- Line esophageal glands, urethra
Transitional
- variable appearance
- relaxed - stratified cuboidal except top layer which tends to be large and rounded
- stretched - flatter and stratified squamous
- multiple layer and elasticity makes it ideal for lining hollow structures
- Allows urinary organs to stretch and maintain protective lining while holding variable amounts of fluid
- Lines urinary bladder and portions of ureters and urethra
What is a gland ?
Single cell or group which secretes a substance into ducts or the surface or into blood.
What are the categories of gland ?
Endocrine or exocrine
Endocrine gland, describe and give example
- Secretes hormones
- Hormones go to interstitial fluid before entering the bloodstream
- Does not enter a duct
- Far reaching effects as can be distributed throughout the body via the bloodstream
- Thyroid, pancreas and ovary
Exocrine gland
- Secretes products into ducts
- Ducts then empty onto the surface of a covering and lining epithelium
- Secretion can have limited effects and can even be harmful
- Pancreas
- Substances include oil, earwax, saliva and digestive enzymes
Can glands be a mix of endocrine and exocrine ? Give example
Yes, pancreas, testes and ovary
What are the structural classification of exocrine glands?
Unicellular glands and multicellular glands.
What are unicellular glands?
Single celled glands
What is an example of a unicellular gland which is also exocrine?
Goblet cells, that secrete mucous directly onto the apical surface of a lining epithelium
Are exocrine glands mostly unicellular or multicellular?
Mostly multicellular, composed of many different types of cells.
Examples of exocrine multicellular gland ?
Sudoriferous (sweat), sebaceous (oi) and salivary glands.
What are the two criteria of multicellular exocrine glands ?
- Whether they are branched or unbranched?
- The shape of the secretory portions of the gland.
Type of branched and unbranched multicellular exocrine glands?
Simple gland - unbranched
Compound gland - branched
Shapes of multicellular exocrine glands?
- Tubular glands - tubular secretory parts
- Acinar or alveolar glands - rounded secretory parts
- Tubuloacinar glands - both round and rounded secretory parts
Describe Simple Tubular
Tubular secretory part is straight and attaches to single unbranched duct.
Example of Simple tubular
Glands in large intestine
Describe Simple branched tubular
Tubular secretory part is branched and attaches to a single unbranched duct
Example of simple branched tubular
Gastric glands
Simple coiled tubular
Tubular secretory part is coiled and attaches to a single unbranched duct.
Example of simple coiled tubular
Sweat glands
Simple acinar/ alveolar
Secretory portion is rounded and attaches to a single unbranched duct.
Example of simple acinar/ alveolar
Glands of penile urethra
Simple branched acinar/alveolar
Secretory portion is branched and attaches to a single unbranched duct.
Example of simple branched acinar/alveolar
Sebaceous glands
Compound tubular
Secretory portion is tubular and attached to a branched duct
Example compound tubular
Bulbourethral (Cowper’s) gland (near prostrate)
Compound acinar/alveolar
Secretory portion is rounded and attaches to a branched duct.
Example of compound acinar/alveolar
Mammary glands
Compound tubuloacacinar
Secretory portion is both tubular and rounded, attaches to a branched duct.
Example compound tubuloacacinar
Acinar/alveolar glands of pancreas
What are the three functional categories of exocrine glands?
- Merocrine glands
- Apocrine glands
- Holocrine glands
How do exocrine glands secretory processes begin?
Begin with endoplasmic reticulum and golgi complex which form intracellular secretory vesicles that contain the secretory products.
Merocrine glands
Secretions synthesized at ribosomes at RER, processed and sorted at GA and released from cells via secretory vesicles.
Which types of functional exocrine gland is most of the glands in the body a type of ?
Merocrine glands
Examples of merocrine glands
Salivary glands and pancreas.
Apocrine glands
Accumulate secretory products at apical surface of secretory cell. Then a portion pinches off via exocytosis from the rest of the cell to release the secretion. The cell repairs itself and repeats the process.
What functional classification of exocrine glands does mammary glands use in the secretion of milk fats ?
Apocrine glands
Holocrine glands
Accumulate a secretory product in their cytosol.
As the secretory cell matures, it raptures and becomes the secretory product. Large amount of lipids from plasma membrane and intracellular membranes in secretory product as rapturing is mode of secretion.
Dead cell replaced by new cell.
What is an example of a holocrine gland?
Sebaceous gland of the skin.
